The short answer, perhaps, is that the eurozone's woes had cast such gloom last year that even the appearance of a few rays of sunlight makes the relative position seem much brighter. And it's true that the US economy has delivered cheerful news of late – jobs are being created, industrial production is up and the housing market seems to be stabilising.

For a fund manager mindful of his career prospects, it's dangerous to miss a turn in the market: if you sat out the 15% rally in share prices since last autumn, you certainly don't want to miss the next 15%. That's how momentum in markets can be generated.

Sceptics, however, smell a potentially disastrous faith in central bankers' ability to create new asset bubbles. After all, even the European Central Bank won't be able indefinitely to give banks a helping hand via its three-year long-term refinancing operation (essentially cheap loans pledged against any old collateral).

Bob Janjuah, Nomura's bearish fixed-income strategist, is worried. "The number of clients who tell me that they know they are being forced into playing a game that will end in disaster, but who feel they have to play along and who hope they will get out before it turns, is a depressingly familiar old tale," he says. You can see his point: this market rally carries a strong whiff of hopeful thinking.